In an optical recording medium on which the information can be recorded, such as a magneto-optical disc, it has been known to provide a helical groove or concentric grooves for tracking in advance on the disc, with the inside of the pre-formed groove or pre-groove or the land between the adjoining pre-grooves being used as a recording track, and to record and/or reproduce the information photomagnetically on or from the recording track along the track direction. That is, the pre-groove is detected optically and the main information is recorded and/or reproduced along the direction of the recording track under application of tracking servo.
In this case, it has been known to record alternately the control information, such as sync signals or addresses, referred to sometimes in this specification as reproduce-only information, and the recording data information per se, on the recording track along the track direction, and to execute data supervision on the basis of the sync signals, addresses etc. of the control information. That is, synchronization of a frame or segment as a unit of data recording is taken by the sync signals, and data are recorded and/or reproduced on the frame-by-frame or sector-by-sector basis with the aid of the address information. As the format for these sync signals and addresses, a so-called CD (compact disc) format, for example, is used in view of interchangeability.
The conventional CD format is explained briefly by referring to FIG. 7.
In this figure, each block or sector as an information recording unit consists of 98 frames of from 0th to 97th frames. The period of each frame is 588T, that is, 588 times the channel clock period T. Each frame is provided with recording regions for frame sync signals, subcode and data inclusive of parity data. A 24T (24 channel bit) frame sync signals region and a 14T subcode region are provided at the leading end of each frame and interconnected by 3T connection bits. In the remaining 544T region, there are arrayed 32 symbols or 32 bytes of sampled data and parity data modulated by the so-called eight-to-fourteen modulation (EFM) system. The frame sync signals include two successive 11T transition intervals to provide an out-of-rule pattern not found in EFM. The 14T subcode region corresponds to one 8-bit symbol.
If an uninitialized optical disc, that is an optical disc on which no data are written, is used, the disc needs to be formatted, that is, sync signals or address information necessary for recording and/or reproduction on or from the optical disc, need to be written along the track direction in the form of, for example, photomagnetic signals.
In the Japanese Patent KOKAI Publication No. 63-87682 (1988), there is disclosed a technique in which the timing code as the address information is included in wobbling signal components of a groove previously formed with wobbling along the track width for tracking (pregroove). For the wobbling signal, a signal which is obtained by frequency modulation of the sinusoidal carrier signal with a frequency of 22.05 kHz, with an absolute time code having a frequency sufficiently lower than that of the carrier signal, is employed. During groove formation on the disc, the groove is wobbled along the track width by the frequency modulated signal for forming the pre-groove in which the absolute time information is included in the wobbling signal. This is abbreviated to ATIP (absolute time in pregroove). During recording/reproduction of the recording data or main data, tracking error signals are obtained from the signals reproduced from the pregroove, while the absolute time codes are demodulated to produce the address information.
With such ATIP technique, detection or processing of signals recorded after frequency modulation is necessarily performed by a dedicated circuit, such that a conventional LSI (large scale integrated circuit) for CDs, for example, cannot be employed. That is, considering that a variety of integrated circuits (ICs) or LSIs, adapted to the pre-existing formats, such as the CD format, are currently presented to the market, it is more desirable that these pre-existing ICs or LSIs be utilizable from the viewpoint that the recording/reproducing apparatus may thereby be lowered in production costs. On the other hand, the information recordable by the ATIP technique is solely the timing code and, if desired to record general data, it becomes impossible to record the timing code, such that the optical pickup cannot be positioned precisely.
On the other hand, since it is convenient both for the user and for the producer supplying the software to the user if the reproduce-only data such as the operating system or basic dictionary are previously recorded on a medium, and such medium is supplied to the user as the above mentioned recordable optical recording medium, there has been proposed and developed a recording medium, such as a disc, on which data may be recorded and the reproduce-only information (ROM information are written previously.
FIG. 8 shows an example of a magneto-optical disc as a recording medium on which the reproduce-only data are recorded previously. In this figure, a magneto-optical disc 1 is provided with a RAM region 2 on which signals may be recorded and a ROM region 3 adapted to be reproduced exclusively. In the RAM region 2, the inside of the previously formed pre-groove or the land between adjacent grooves is reserved for the recording track 4, and the information is photomagnetically recorded on this recording track 4. In the ROM region 3, there is provided a track 5 in which reproduce-only data are previously recorded (preformatted) in the form of pits or the like.
With such a magneto-optical disc 1, since the recordable RAM region 2 and the reproduce-only ROM region 3 are separated from each other, the recordable capacity on the overall disc surface is diminished by an amount equal to the area of the ROM region 3.
On the other hand, control data such as sync signals or the address information for facilitating the accessing during recording/reproduction need to be included in the main information recorded in the RAM region 2. For example, in the case of a format in which frame synchronization is taken at each 588T frame, T being a channel bit period, in accordance with the CD format (format for compact disc), a 24T sync signal part having a pattern of two successive lit transition periods and a 14T subcode part connecting to the sync signal part by 3T connecting pits are provided at the leading end of each frame, as shown in FIG. 8, and the remaining 544T data with the interposition of the 3T connecting bits provide the data proper inclusive of parity bits. Thus a 44T region of the 588T region of each frame cannot be used for recording the data per se.
The present invention has been made in view of the foregoing. It is an object of the present invention to provide an optical recording medium and a method for data recording/reproducing wherein the IC or LSI adapted for a widely employed format, such as the pre-existing CD format, may be employed directly.
It is another object of the present invention to provide an optical recording medium and a method for information recording/reproduction, wherein the information recording capacity of the optical recording medium, on which reproduce-only data have been recorded in advance by offsetting along the track width, may be increased, the circuitry for recording/reproduction on or from the recording medium may be simplified and the preexisting format may be utilized directly.